Mobile communication systems have been developed to provide a communication service to users while they are moving. With the rapid development of technology, mobile communication systems have been developed to provide data communication services at a high speed as well as voice communication.
In order to meet the increase in the demand for wireless data traffic after the commercialization of 4G communication systems, considerable effort has been made to develop pre-5G communication systems or improved 5G communication systems. This is one reason why ‘5G communication systems’ or ‘pre-5G communication systems’ are called ‘beyond 4G network communication systems’ or ‘post LTE systems.’
In order to achieve a high data transmission rate, 5G communication systems are being developed to be implemented in a band of extremely high frequency, or millimeter wave (mmWave), e.g., a band of 60 GHz. In order to reduce the occurrence of stray electric waves in a band of extremely high frequency energy and to increase the transmission distance of electric waves in 5G communication systems, various technologies being explored, for example: beamforming, massive MIMO, Full Dimensional MIMO (FD-MIMO), array antennas, analog beam-forming, large scale antennas, etc.
In order to improve system networks for 5G communication systems, various technologies have been developed, e.g.: evolved small cell, advanced small cell, cloud radio access network (cloud RAN), ultra-dense network, Device to Device communication (D2D), wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), interference cancellation, etc.
In addition, for 5G communication systems, other technologies have been developed, e.g., Hybrid FSK and QAM Modulation (FQAM) and Sliding Window Superposition Coding (SWSC), as Advanced Coding Modulation (ACM), Filter Bank Multi Carrier (FBMC), non-orthogonal multiple access (NOMA), sparse code multiple access (SCMA), etc.
Meanwhile, unlike voice services, data services are allocated resources, etc., depending on a channel status and an amount of data to be transmitted. In wire communication systems such as mobile communication systems, schedulers perform transmission resource management, such as allocation of transmission resources, etc., considering the amount of resources for transmission, the channel status, the amount of data, etc. These are also carried out in the same manner as LTE as one of the next generation mobile communication systems, and a scheduler located in a base station may manage and allocate wireless transmission resources.
Mobile communication systems have been developed to provide voice call services, supporting users' mobility. With the development of communication technology, mobile communication systems have recently been evolved to such an extent that they provide data communication services at a high data transfer rate. However, as mobile communication systems evolve to provide more various services, they face lack of resources and users' demands for high speed data services. Therefore, the development of more advanced mobile communication systems is required.
In order to meet the demand, Long Term Evolution (LTE) that has been developed as a next generation mobile communication system is in process of standardization by the 3rd Generation Partnership Project (3GPP). LTE is a technology that is being developed to be commercialized in about 2010, implementing high speed packet-based communication with a transmission rate of maximum 100 Mbps. To this end, various proposals have been discussed. For example, a scheme has been proposed to reduce the number of nodes on communication paths by simplifying network architecture. Another scheme has been proposed to apply wireless protocols to wireless channels as close as possible.
Communication systems include: a downlink (DL) transmitting signals from transmission points, such as Base Stations (BSs) or NodeBs, to User Equipments (UEs, terminals); and an uplink (UL) transmitting signals from UEs to reception points such as NodeBs. User Equipment (UE) is also referred to as a mobile station. The UE or a mobile station is fixed or mobile. Examples of the UE or a mobile station are a mobile phone, a personal computer, etc. NodeB is referred to as a fixed station or an access point. NodeB may also be called any other name equivalent thereto.
DL signals include: data signals containing information content, control signals, and Reference Signal (RSs) known as pilot signals. A NodeB transmits, to UEs, information on data via Physical Downlink Shared Channels (PDSCHs), and control information via Physical Downlink Control Channels (PDCCHs). UL signals include: data signals, control signals, and RSs. The UEs transmit, to NodeBs, information on data via Physical Uplink Shared Channels (PUSCHs), and control information via Physical Uplink Control Channels (PUCCHs). A UE may also transmit data information and control information via the PUSCH.
The LTE system, as a typical example of the broadband wireless communication systems, employs Orthogonal Frequency Division Multiplexing (OFDM) on the downlink and Single Carrier-Frequency Division Multiple Access (SC-FDMA) on the uplink. The multiple access scheme performs allocation and management of time-frequency resources to carry data and control information according to users, so as not to overlap with each other, i.e., so as to achieve orthogonality between them, thereby distinguishing data or control information between respective users.
The LTE system employs a Hybrid Automatic Repeat reQuest (HARQ) scheme for retransmitting data, which has failed in decoding in the initial transmission, via the physical layer. HARQ is a scheme that allows a receiver to transmit, when not correctly decoding data from a transmitter, information (NACK) indicating the decoding failure to the transmitter so that the transmitter can perform re-transmission of the data from the physical layer. The receiver combines the data re-transmitted from the transmitter with the existing data for which decoding has failed, thereby increasing the capability of data reception. When correctly decoding data, the receiver transmits information (ACK) indicating the success of decoding to the transmitter so that the transmitter can perform transmission of new data.
In broadband wireless communication systems, one of the important factors in providing high transmission rate wireless data services is the ability to support scalable bandwidths. For example, LTE systems are capable of supporting various bandwidths, such as 20/15/10/5/3/1.4 MHz, etc. Therefore, service providers are capable of selecting a particular one of the various bandwidths and providing services via the bandwidth. There are various types of User Equipments (terminals) that are capable of supporting bandwidths from a minimum of 1.4 MHz to a maximum of 20 MHz.
LTE-Advanced (LTE-A) systems, aiming to provide a level of service for IMT-Advanced requirements, are capable of providing services in broadband up to a maximum of 100 MHz, by carrier-aggregating LTE carriers. LTE-A systems require a band broader than that of LTE systems for high-speed data transmission. In addition, LTE-A systems need to allow for the backward compatibility with LTE terminals, so that the LTE terminals can access and receive the services of the LTE-A systems. To do this, LTE-A systems divide the entire system bandwidth into sub-bands or component carriers (CC), through which the LTE terminals are capable of transmission or reception, and aggregate part of the component carriers. LTE-A systems are capable of creating data according to respective component carriers and performing the transmission of the created data. LTE-A systems are capable of high speed data transmission through the transmission/reception processes of the legacy LTE systems used according to the respective component carriers.
In recent years, a method of transmitting signal via a femto-NodeB has been proposed in order to provide a UE with services in a confined space, such as an indoor space of a building. When the femto-NodeB performs the transmission of signals, the channel status may differ from that of a macro base station. Therefore, the femto-NodeB needs a transmission method and apparatus to meet the channel status.